The present invention relates to a click stop mechanism provided in the aperture preset ring of an interchangeable lens.
A click stop mechanism has been employed for an interchangeable lens in which a click ball urged by a spring is engaged with rectangular or V-shaped grooves in the aperture preset ring to stop the ring with a click (hereinafter expressed as "a click-stop" when applicable). A photographing operation is carried out by turning the aperture preset ring to a desired aperture value (manual aperture value) in a manual aperture preset range according to the photographic intent and available lighting. In the case of a lens used in a shutter speed priority automatic exposure system, that is, in the case of a so-called "EE lens", in addition to the above-described manual aperture value positions an automatic aperture preset position "A" or "EE" ("A" position) is provided and a click stop groove is provided therefor. For selecting a manual aperture value, the aperture diameter of the lens is set by turning the aperture preset ring. For the "A" position, it is set by the automatic exposure control mechanism in the camera body. Although the two click stop grooves are provided in the same aperture preset ring, they have completely different functions.
In order to clearly distinguish the operation of switching the manual aperture value position over to the "A" position from the operation of switching the "A" position over to the manual aperture value position, heretofore the click grooves were made deeper or additional click grooves were provided for the manual aperture value position and the "A" position to thereby increase the click-stop. Using this technique, switching can be clearly detected due to the increased click-stop load. However, there is a drawback in that the operation of turning or switching, the aperture preset ring requires a relatively large force.
In addition, a technique is known in the art according to which means for stopping switching over from the manual aperture value position to the "A" position and vice versa is provided wherein switching is permitted only by operating one of two separate release means. However, thus technique is also disadvantageous in the following point: If, because of the structure of a camera, dimensional requirements such as an angle required for the switching operation are not sufficiently satisfied, the components of the stopping means will have an insufficient strength. If a strong force is inadvertently exerted on the aperture preset ring when the interchangeable lens is engaged with or disengaged from the camera body, the components of the stopping means may be damaged.
Accordingly, an object of the invention is to provide a click stop device for an aperture preset ring which, in switching over the manual aperture value position to the "A" position and vice versa, will not be damaged, even if a large force is applied thereto when the lens is engaged with or disengaged from the camera body, and in which a click stop load for detecting the switching operation is reduced.